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Hopefully this information will make the use of a PID less intimidating. Just got my PID setup and going and is it so cool. I have 40 gallon water heater setup with two 3500 watt elements. I ordered the PID ($45) and dual relays. The PID salesman did the math and calculated the draw of each element to be 17 amps and suggested 25 amp Solid State Relays (SSR).About $15 US each. Things that I learned the hard way: 1) Install a fast acting fuse (25 amp in my case) close to the relay. Why you ask, because when the elements are connected, as they are in a traditional WH setup minus the thermostat, the draw is 38 amps. That is 1.5 times the amps rated for my relays. The fireworks and smell of an electrical overload were awesome. 2) Solution is to have each element on its own circuit. 3) SSR’s get hot. Solution I bought a heat sink with fan at the computer parts store for $15 and used the power supply from an old computer to power the new fan and have no heat problems. It would also be a good idea to install a fuse inline on the power wire for the PID unit itself.
The small terminals on the back of your PID will be wired to the SSR and any small wire will work. My output is 3 millivolts. And SSR’s could be wired in parallel if more than one is necessary. Be sure and read the literature that came with your PID as there are many settings that will be particular to you. Such as: specific thermocouple, temperature offset if thermocouple is not reading correctly, alarms that switch on at specific temperature (too hot). On my unit the alarm function acts as a switch. My plan is to wire 110 volt power side and terminate into a wall plug and plug in a radio with the volume up, when I hear the radio time to look at the temp. The PID can switch the SSR on and off a 100 times per second. With the water heater being very well insulated, my system may only need power 8 out of those 100 times. The down side of using a water heater is the limitation of opening on top. Mine is 1 inch opening with a 2 inch column on top. Hope this will save some headache and dollars.
PS I think that pieces of this thread should be added to the control section of this site. Just my $0.02

Why did you opt for SSR's instead of solid contact realys? Sounds like a hassle having to cool them down.

Swag wrote:Why did you opt for SSR's instead of solid contact realys? Sounds like a hassle having to cool them down.

true, but the ssr's have a better responce time. besides who want's to listen to "clack clack clack" for hours on end

The heat is only an issue until the still is at operating temperature, then the SSR's are only operable for very short period of time.
Also, the initial cost of the set up is less than that of a reostat, and combined with the accuracy of temperature control. For me it was a no-brainer